Alloy steels



United States Patent 3,497,399 ALLOY STEELS George A. Roberts, Champion, and John C. Hamaker,

Jr., Latrobe, Pa., assiguors to Vasco Metals Corporation, Latrobe, Pa., a corporation of Pennsylvania No Drawing. Continuation-impart of application Ser. No. 337,179, Jan. 13, 1964. This application July 13, 1966, Ser. No. 564,731

Int. Cl. C22c 39/ 52 US. Cl. 148-3 11 Claims ABSTRACT OF THE DISCLOSURE A new hardened alloy steel composition having up to 3.4% chromium and up to cobalt and tungsten, molybdenum and vanadium in the approximate amounts existing in the essentially martensitic matrix of a hardened high speed steel having an approximate analysis of chromium+tungsten+vanadium+2 times molybdenum in excess of 13.5%, a room temperature hardness of about Rockwell C 60 and above, a hot hardness of about Rockwell C 45 and above at about 1000 F. and more than about 5% undissolved excess carbides, said compo sition approximating said matrix limits of 35% for compositional elements with nominal contents of from 1 to 5%, :.25% for compositional elements with nominal contents of 1% or less, and with the carbon content ranging from about 20% to about .80%, said composition after hardening consisting essentially of an essentially martensitic structure containing less than about 5% excess carbides. These alloys are prepared by reducing the chromium content of the parent steel to at least 3.40% and hardening the reduced cobalt alloy by substantially the same heat treatment procedures used to harden the high-temperature steel.

This application is a continuation-in-part of application Ser. No. 337,179, filed Jan. 13, 1964, now abandoned.

This invention relates to a new class of steels and to methods of making such steels.

Under the microscope, hardened high speed steel is found to consist essentially of two phases: extremely hard excess alloy carbides and a matrix or background material. This aggregate of excess carbides and matrix material provides probably the highest strength properties currently available in any material as evidenced by the articles entitled, The Bend Test for Hardened High Speed Steel, by Arthur H. Grobe and George A. Roberts, Transactions of the American Society for Metals, vol. 40, 1948, pp. 435-490, and Bend: Tensile Relationships for Tool Steels at High Strength Levels, by John C. Hamaker, Jr., Vance C. Strang and George A. Roberts, Transactions of the American Society for Metals, vol. 49, 1957, pp. 550-575. High speed steels while possessing high hardness and strength properties suffer from the disadvantage of being brittle. U1tra-high strength structural steels, on the other hand, are tough and ductile but are not as strong or hard as the high speed steels. Steels with the strength and hardness of high speed steels and the toughness and ductility of ultra-high strength steels will therefore fill a long felt need in the art.

3,497,399 Patented Feb. 24, 1970 An object of our invention is to provide a new family or class of steels of this nature, characterized by the fact that they have the same approximate hardness of high speed steel and the same approximate toughness and ductility of ultra-high strength steels.

Another object of our invention is to provide a new method of making such steels according to which the desired degrees of hardness, toughness and ductility may be conveniently and economically attained.

Other objects and many of the attendant advantages of our invention will be readily appreciated as the same become better understood by reference to the following detailed description when considered in connection with the accompanying tables.

For many years, various academic studies have been conducted to determine the composition of high speed steels. The work of Grossman and Bain is summarized in their book High Speed Steel, copyright 1931, by John Wiley and Sons. Other recent studies are summarized in the following paper: The Effect of Vanadium and Carbon on the Constitution of High Speed Steel, by Donald J. Blickwede, Morris Cohen and George A. Roberts, Transactions of the American Society for Metals, vol. 42, 1950, pp.'11611196. With the improved methods of determining the excess carbide analysis and content in high speed steels, the matrix compositions can be determined with acceptable accuracy, thus opening a new area for research and development. In our copending application, now US. Patent No. 3,117,863, issued Jan. 14, 1964, we described a new class of steels based on the matrix compositions of high speed tool steels containing chromium.

We now have unexpectedy discovered that new steels having compositions which correspond to the compositions of the matrices of heat treated high speed steels from which some or all chromium has been omitted may be heat treated to produce a new class of steels having the same approximate toughness and ductility of ultrahigh strength steels and approaching the strength and hardness of high speed steel. It was unexpectedly found that the hardening, tempering, grain size and preliminary toughness characteristics of the new steels of this invention are quite similar to those of the matrix steels described in our above-identified patent. We furthermore discovered that the omission of some or all chromium provides a hardenability control that may permit case and core applications Where shock resisting cores are required with hard, wear resistant cases, for such tooling applications as cold heading dies, pneumatic hammers, etc. Heretofore, only the straight carbon or very low alloy, water hardening steels have been used for these applications. Thus, this invention would permit the widespread use of the much more highly alloyed compositions with their greater potential wear resistance, hot hardness and toughness. Heretofore, when greater wear resistance and hot hardness are required, insert dies, employing a high speed steel die inserted in a tough casing material such as an H11, 12 or 13 hot work die steel, were being used. The compositions of the new matrix steels described herein may well replace the inserted dies for such special applications, and thus greatly extend the usefulness of case and core materials like the water hardening steels to higher temperatures (carbon steels have no particular heat resistance) and for greater wear resistance. Additionally, omission of some or all chromium permits simplifications of the alloy steel without sacrificing beneficial properties thus reducing manufacturing ditficulties and production costs, Higher toughness prop erties may be obtained or better combinations of toughness, strength and hardness for both ultra-high strength structural and tooling applications may be obtained. It was also unexpectedly discovered that reductions rather than omission of the chromium content below those specified for the matrix steels in the above-identified patent, e.g., from trace amounts up to about 3.4%, or particularly 2%, also can provide the above-described advantages.

When proceeding according to our present invention, a heat treated high speed steel is preselected which has the strength and hardness characteristics that are desired in our finished structural composition. The high speed steels alluded to in this application are described as steels having essentially martensitic matrices, with room temperature hardness of about Rockwell C 60 and above, hot hardness of about Rockwell C 45 and above at about 1000 F. and which contain more than about 5% undissolved excess carbides. These high speed steels are usually hardened at temperatures above 2000 F. when processed. Owing to the inclusion of excess carbides throughout the structure of the high speed steels, the preselected steel is generally too brittle for structural use. The chromium content of the preselected high speed steel is reduced or omitted and the matrix composition of the resulting material, hereinafter called the parent material, is determined by the analytical methods referred to above. Thereafter, a new melt is prepared, the chemical analysis of which corresponds to the matrix composition of the parent material, i.e., the selected high speed steel less the chromium content thereof. Alternatively, the matrix composition of the preselected hardened high speed steel itself can be determined and a new melt prepared having the same chemical analysis of the matrix composition, except that chromium is reduced or omitted. The new composition or melt is preferably made by a vacuum melting method although it is possible to employ air melting methods presently used in the industry. Of the vacuum melting methods available, applicants prefer to make the composition by the consumable electrode vacuum melting technique.

The chemical analysis of our new steel is such that essentially all of the carbides which are customarily present in excess quantities in the annealed or softened preselected steel, or the annealed or softened parent material, will be dissolved in our steel when the latter is heated for hardening. The resulting steel throughout closely resembles the matrix of the parent steel or parent material in structure without the inclusion of excess carbides. Ingots of our new steel are then cast and the steel is processed and heat treated essentially in accordance with the normal specifications of the preselected high speed steel. The steel thus produced is more ductile and tougher than the preselected steel or the patent material and yet possesses higher hardness than normal structural steels. However, the absence of excess carbides permits grain boundary movement during heat treatment which results in grain coarsening. To obtain a fine grain size essential to maximum toughness and ductility in the new composition, the hardening temperature should be lowered about 175 F., or alternatively, to a point where a slight amount of excess carbide is produced for restricting grain growth. In any event the lower hardening temperature selected is such that less than 5% undissolved excess carbides are present in the hardened essentially martensitic matrix. Thus we obtain a new composition which closely resembles the matrix of the preselected high speed steel, yet is considerably tougher and more ductile at substantially high hardness levels.

Listed below are several high speed steel compositions which fall within ranges of high speed steels commercially available, together with corresponding chromium-free parent materials and matrix compositions corresponding to the matrices of said parent material. The percentage of iron in each composition is substantially the remainder in each case. It should be understood that the compositions listed below are typical examples of innumerable compositions falling within the scope of the invention and the invention is not to be construed as limited to the specific compositions about to be discussed since there are several dozen high speed steels commercially available such as the high speed steels and high speed steel classes set forth on page 21 of Metals Handbook, 1954 Supplement, on pages 15 and 22-29 of the Steel Products Manual on Tool Steels published April 1963 by the American Iron and Steel Institute, New York, N.Y., and the Supplementary Information for pages 15 and 26 thereof published May 1963, and in the booklet entitled Classification and Symbols for Indentification of High Speed Steels, by the Gorham Tool Company, Detroit, Mich.

TABLE I Chromium-Free Chromium-Free Parent Matrix Material Compositions Example 1M-1 Type:

C b 79 55 Silicon 20 21 Manganese 21 20 S111 014 006 Phosphorus 003 004 Tungsten 1. 56 92 Molybdenum 8. 97 5. 19 Vanadium 1. 21 95 Example 2M2 Typ Carbon. .88 .50 Silicon 19 19 Manganese--.-. 22 l8 Sul 010 008 003 004 6. 21 1. 82 5. 07 2. 63 1. 84 93 87 53 30 28 20 23 02 007 Phosphorus 02 004 Molybdenum- 8. 25 5. 49 Vanadium 1. 90 l. 11 Example 4-M-36 Type Carbon 55 Silicon 19 21 Manganese.- 22 15 Sulphur 02 013 Phosphorus-.-. 0. 2 003 Tungsten 6. 0 2. 02 Molybdenum 5. 0 2. 60 Vanadium... 2. 0 95 all; 8. 0 7. Example 5-M-42 Type ar on 1. 07 55 Silicon 22 16 Manganese-.- 22 22 Sulphur 02 015 Phosphorus. 02 003 Tungsten... 1. 50 1.00 Molybdenum 9. 50 5. 00 Vanadium... 1.15 92 Oobalt...- 8. 00 7. 95 Example 6-T-1 Type:

arbon 73 50 Silicon 32 18 Manganese... 20 18 Sulphur O2 006 Phosphoru 02 003 Tuugsten.. 18. 00 8. 45 Molybdenum. 21 Vanadium 1. 00 97 The nominal analysis of the Cr-free parent materials which correspond except for Cr to the composition of the preselected steel may vary il% for nominal contents of 5% or greater, i.5% for nominal contents of from 1% to 5%, and i.25% for nominal contents of other elements, such as silicon and manganese, which are present in quantities of less than 1.0%. Such variations lie within the contemplation of the invention. In general the carbon content for the new class of steels generally varies from .20 to .80% for the entire class while remaining within the scope of the invention. Once the matrix composition of a Cr-free parent material is determined, it will serve as a target for the production of our compositions which may vary somewhat during processing, as

indicated. The matrix steels of the present invention include those which correspond in composition, except for chromium content, to the essentially martensitic matrix of a hardened high speed steel, the high speed steel having a composition of tugnsten-l-vanadium-l-Z times the 6 Austenitizing temperatures of 2050 F. and 2025 F. were selected for further tempering study and comparison and the austenitizing procedure employed for the asquenched hardness samples was kept the same. All samples were austenitized for min. and oil quenched 5 molybdenum of 13.5%, preferably 17%. from the two austemtlzing temperatures. Rockwell C To demonstrate the results obtamed when proceeding hardness readings were taken after each tempering cycle according to our invention, a detailed discussion of the for the various tempering temperatures, and are listed beproperties; treatment and composition of the typical 10w i T bl III, steels described above will now be given. 10 TABLE III ROCKWELL on HARDNESS (AVERAGE OF The preselected hlgh speed Sleds f? a hafden- FIVE READINGS) MEASURED AFTER EACH OF THREE mg range and have relatively hlgh ductllity at high hard- W -H UR TEMPERS ness levels when compared to the general class of high Austem-tized 2,0255 F Austenitized ZOWR speed steels. In general, such steels are usually heat g p g t s (1 d F t S d d emper llS 8C0. 11 HS econ 1r treated 1n accordance with the respectlve schedules set 15 tum'o F. Temper Temper Tempe, Temper Temper Temper forth in the above-mentioned Steel Products Manual to E l obtain their normal high hardnesses. 5gf 5 58 5 59 5M 60 A melt was made corresponding to each Cr-free matrix 52.2 56 57 57.5 composition specified hereinbefore. Each melt was cast :1: 2 5 5 ,5; 22;? 22:? into a 100 pound ingot. The ingot was then forged at the gig-"- g 2 same temperatures as the corresponding preselected high 5 555 57 2 1,025... 57.5 57.5 53 57 59.5 59.5 speed steel 16 customarily forged, and rolled In rolling, 50m" 575 58.5 58 59.5 60 5 605 the matrix steel was treated like a hot work die steel and 1,100 59 53.5 57.5 59.5 59.5 59 no difficulties were encountered. A bar, 10 feet long, i gg g 2? 22-2 was selected and subjected to high speed annealing, at 25 E 1,311 41 37 55.5 41 37.5 35 about 1625 F. From this annealed stock, cubes were 3 5 5 515 5 5 515 e m e r at 500 55.5 56.5 56.5 56 56 56 selected and pr heated at a te p ratu e 1 500 F The 700"0 53.5 54 5k 5 55.5 54.5 55 samples were austenitized in a gas-fired, semr-mufile type 900 53,5 3 54 4,5 5.5 4 950 53.5 54.5 55 54.5 55 55 furnace for five minutes at various temperatures and oil 53.5 5 5&5 555 55.5 55 quenched or salt quenched. The as quenched hardness and 1,030"-.- 54.5 55.5 55.5 56 57 57.5 intercept grain results for both oil quenched and salt 18 3:: 2 gg 53 quenched samples from various temperatures, together -5 58 58 57.5 a 1,150.... 56.5 56 55 57 57 56.5 with the hardness figures after each tempering at 1000 55 525 515 56 525 F. for two hours, are set forth in Table II below. 41 3 3555 43 TABLE II.ROCKWELL C HARDNESS (AVERAGES FROM FIVE READINGS) Salt Quenched Oil quenched Intercept Grain Size, Austenitizing As First Second Third As First Second Third Salt Temperature, F. Quenehed Temper Temper Temper Quenched Temper Temper Temper quenched Example 1 1,9 39 42. 5 43 43 56 54. 5 55 55. 5 1,975 40 42. 5 45 55. 5 54. 5 56. 5 56. 5 2,000 42 44. 5 46. 5 47. 5 57 57 57 57 2,025 42. 5 46 4s. 5 48. 5 58. 5 57 57 57. 5 ,050 43. 5 48 51 59 57 58 5s. 5 2,100 46 51 53. 5 54.5 61. 5 55. 5 59. 5 59. 5 2,150 43. 5 54. 5 56. 5 57. 5 61. 5 58. 5 61. 5 61. 5 2,20 51 56. 5 5s. 5 59 61 62 64 Example 2 43. 5 46 47. 5 4s 42. 5 44. 5 46 46. 5 44. 5 46.5 49. 5 50 45 47 50 50.5 44. 5 47. 5 50 50. 5 45. 5 4s. 5 50. 5 51. 5 45. 5 49 51. 5 52. 5 46. 5 49. 5 51. 5 52. 5 45. 5 50. 5 52 53 48. 5 52.5 54 54. 5 46. 5 52 54. 5 55. 5 51. 5 55 56. 5 5s. 5 9. 5 47. 5 54. 5, 57 5s. 5 53. 5 5s 60 61. 5 6. 5 46 55. 5 57. 5 59 56. 5 60. 5 62. 5 63 6. 5

45. 5 49 51. 5 52 61. 5 57. 5 5s. 5 59. 5 5. 5 46 49. 5 51. 5 52.5 61 57. 5 59. 5 59. 5 4. 5 46 49. 5 51. 5 52. 5 62. 5 57. 5 59 59. 5 4 46. 5 50 52 53. 5 61. 5 53. 5 59. 5 60 4 47. 5 51 53 54 62. 5 5s. 5 60 60 3 4s. 5 52 53. 5 54. 5 61. 5 59 59. 5 60 2. 5 4s 52 53. 5 55 61. 5 59 60 60 2. 5

TABLE Ill-Continued Austenitized 2,025 F. Austenitized 2,050 F.

Temperlng Tempera- First Second Third First Second Third ture, F. Temper Temper Temper Temper Temper Temper 1,300..- 47 43 43 48 44. 5 43 Example 5:

In conclusion, our new matrix steels fill a gap between the ultra-high structural steels, which are limited to about 57 Rockwell C hardness and the very strong but brittle standard high speed steels which can be heat treated to 65 Rockwell C or greater. In this sense our new class of steels may be regarded as intermediate high strength and high speed steels, which possess room temperature hardness ranging from in excess of Rockwell C 57 and up to about Rockwell C 62, while possessing high ductility after austenitizing and tempering.

Despite the high molybdenum and tungsten contents, which would be expected to enhance the depth of hardenability considerably, the chromium-free matrix steels of the examples show a depth of hardenability limitation. In fact, the somewhat slower salt quench resulted in definitely lower as quenched and tempered hardnesses than an oil quench for all of these steels. This limited hardenability should make the chromium-free matrix steels useful for applications requiring a hard, strong, wear resistant surface, backed up by a softer, more ductile, tough core, such as in pneumatic hammers or for cold heading dies, in which the working surface has a high hardness, while the underlying supporting material has a lower hardness level but a greater toughness.

It will be seen that the objects and advantages set forth above among those made apparent from the preceding description are efficiently attained and, since certain changes may be made in the compositions and in carrying out the above process without departing from the scope of the invention, it is intended that all matter contained in the above description and set forth in the accompanying tables shall be interpreted as illustrative and not in a limiting sense.

Advantages are also obtained from each of the following matrix compositions which were made in a manner similar to the previously described matrix compositions. As a result, matrix compositions corresponding to the martensitic matrices of parent materials which correspond in composition to high speed steels wherein the chromium content has been reduced to less than 3.4% and the Cr+W+V+2 times Mo are 13.5%, preferably 17%, or more, provide advantages similar to those set forth hereinbefore.

TABLE IV Parent Matrix Material Compositions Example 7-M-1 Type:

Car on 81 52 Silicon .31 .28 Manganese 25 19 Sulphur.. .015 012 Phosphorus 007 005 Tungsten 1. 58 1.03 Molybdenum. 8. 79 5. 08 Vanadium 1. 14 99 C hromium 2. 07 1. 97 Example 8-M-2 Type Carbon 85 52 Silicon. 33 18 Manganese 24 20 Sulphur. 013 .010 Phosphorus 006 007 Tungsten..- 6. 15 2. l1 Molybdenum. 5. 00 2. 84 Vanadium 1.86 1. 00 Chromium 2. 04 2. 04 Example 9M10 Type:

C b 87 54 30 28 20 24 Sulphur 02 014 Phosphorus. 02 005 Molybdenum 8. 25 5. 46 Vanadium 1. 90 1. 13 2. 00 1.

80 58 19 29 Manganese 22 24 Sulphur. 02 010 Phosphorus 02 004 Tungsten 5. 00 1. 95 Molybdenu.rn 6. 00 2. 82 2. 00 97 8. 00 8. 00 2. 00 2. 07

. 73 55 32 25 20 18 p 02 011 Phosphorus. 02 008 Tungsten." 18. 00 8.70 Molybdenum. 24 Vanadium 1. 00 l. 00 Chromium 2. 00 1. 94

Listed below are several compositions based on high speed steel compositions and in which chromium content has been reduced to approximately 2% and other additions, such as, cobalt (Examples 13 and 14) and silicon (Examples 16 and 17), have been made for further special or enhanced properties.

TABLE VIb.-ROOKWELL C HARDNESS (AVERAGES FR( M FIVE READINGS) Intercept Grain Size, .Austemtlzing Temperature, Salt 11 Salt F. Quenched Quenched Quenched Austenitizing temperatures X and Y were selected for further tempering study and comparison and the austenitizing procedure employed for the as quenched hardness samples was kept the same. Samples of Examples 7, 8, 11, and 14 through 17 were austenitized at 2050 F. (X) and 2100 F. (Y). Example 9 was austenitized at 2100 F. (X) and 2150" F. (Y). Example 12 was austenitized at 2150 F. (X) and 2200 F. (Y). Example 13 was austenitized at 2000 F. (X) and 2050 F. (Y). The samples of Examples 7-9 and l214 were austenitized in each case for 2 /2 minutes. The samples of Examples 11 and 1517 were austenitized for 5 minutes in each case. The samples of Examples 7-9 were salt quenched from the austenitizing temperatures and the samples of Examples 11-17 were oil quenched from the austenitizing temperatures. Rockwell C hardness readings were taken after each tempering cycle for the various tempering temperatures and are listed in Table VII.

Austenitized X, F.

Austenitized Y, F.

Tempering Tempera- First" Second Third First Second Third ture, F. Temper Temper Temper Temper Temper Temper Example 7:

Austenitized X, F. Austenitized Y, F. Tempering Tempera- First Second Third First Second Third ture, F. Temper Temper Temper Temper Temper Temper 57. 1 56.5 56.8 57. 7 57. 1 56.8 55. 3 56 55. 4 56. 4 57 55. 8 56. 4 56. 7 57 56. 9 57 57 57. 5 57. 9 57. 8 59 58. 6 58. 8 56.8 57 57 58 58 58. 3 57. 3 56. 6 56. 2 58 57. 7 57. 1 56. 7 55.2 55 57. 5 57 56 54 51. 6 50. 5 54. 8 53. 3 52 50. 4 46. 5 44 51. 5 47. 3 46. 5 1,300.-. 42 37. 5 34 43. 4 38. 8 35. 8 Example 16:

Examples 13 and 14 illustrate that additions of up to 10% cobalt to alloy steel compositions corresponding to parent steels not normally containing substantial amounts of cobalt, e.g., M-1 and M-2 steels, provide further advantages such as the improvement in strength properties. Examples 16 and 17 illustrate that additions of silicon above those levels normally found in the parent steels increase the peak hardness. Such silicon additions also increase maximum strength and provide improved ductility at elevated temperatures.

In conclusion, our new matrix steels fill a gap between the ultra-high structural steels, which are limited to about 57 Rockwell C hardness and the very strong but brittle standard high speed steels which can be heat treated to 65 Rockwell C or greater. In this sense our new class of steels may be regarded as intermediate high strength and high speed steels, which possess room temperature hardness ranging from in excess of Rockwell C 57 and up to about Rockwell C 62, while possessing high ductility after austenitizing and tempering.

Despite the high molybdenum and tungsten contents, which would be expected to enhance the depth of hardenability considerably, the reduced chromium matrix steels of the examples show a depth of hardenability limitation. In fact, in almost all cases, the somewhat slower salt quench resulted in definitely lower as quenched and tempered hardnesses than an oil quench for these steels. This limited hardenability should make the reduced chromium matrix steels useful for applications requiring a hard, strong, wear resistant surface, backed up by a softer, more ductile, tough core, such as in pneumatic hammers or for cold heading dies, in which the working surface has a high hardness, while the underlying supporting material has a lower hardness level but a greater toughness.

Cobalt in amounts up to 10% When added to the compositions of this invention increases tensile strength and increases hardness.

It will be seen that the objects and advantages set forth above among those made apparent from the preceding description are efficiently attained and, since certain changes may be made in the compositions and in carrying out the above process without departing from the scope of the invention, it is intended that all matter contained in the above description and set forth in the accompanying tables shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A method of making a new alloy steel comprising the steps of, reducing the Cr content to at least 3.4% of essentially martensitic matrix of a high speed steel having a composition of chromium-l-tungsten+vanadium+2 times the molybdenum in excess of 13.5%, a room temperature hardness of about Rockwell C 60 and above, a hot hardness of about Rockwell C 45 and above at about 1000 F. and more than about undissolved excess carbides, said composition approximating said matrix limits of 11% for composition elements with nominal contents of 5% or greater, 125% for compositional elements with nominal contents of from 1 to 5%, -.25% for compositional elements with nominal contents of 1% or less, and with the carbon content ranging from about .20% to about .80% and hardening the prepared composition at substantially the same hardening temperature employed for hardening the high speed steel having an unreduced Cr content.

2. A method of making a new alloy steel comprising the steps of, reducing the chromium content of to at least 3.4% of a composition corresponding approximately to the chemical constitution of the essentially martensitic matrix of a hardened high speed steel having a cornposition of chromium+tungsten+vanadium+2 times the molybdenum in excess of at least about 17%, a room temperature hardness of about Rockwell C 60 and above, a hot hardness of about Rockwell C 45 and above at above 1000 F. and more than about 5% undissolved excess carbides, and hardening the prepared composition at substantially the same hardening temperature employed for hardening the high speed steel.

3. The method of claim 2 further defined in that said matrix composition is hardened at a lower hardening temperature so that undissolved excess carbides are formed,

said lower hardening temperature being such that less than 5% undissolved excess carbides are formed.

4. The method of claim 2 further defined in that the chemical composition of the essentially martensitic matrix varies within the following limits:

i1% for compositional contents of 5% or greater, i.5% for compositional contents of from 1 to 5 and i.25% for compositional contents of 1% or less.

5. A hardened alloy steel composition consisting essentially of the constituents of up to 3.4% chromium and up to 10% cobalt and tungsten, molybdenum and vanadium in the approximate amounts existing in the essentially martensitic matrix of a hardened high speed steel having an approximate analysis of chromium-itungsten-l-vanadium-l-Z times molybdenum in excess of 13.5%, a room temperature hardness of about Rockwell C and above, a hot hardness of about Rockwell C 45 and above at about 1000 F. and more than about 5% undissolved excess carbides, said composition approximating said matrix limits of 11% for compositional elements with nominal contents of 5% or greater, :.5% for compositional elements with nominal contents of from 1 to 5%, 325% for compositional elements with nominal contents of 1% or less, and with the carbon content ranging from about .20% to about .80%, said composition after hardening consisting essentially of an essentially martensitic structure containing less than about 5% undissolved excess carbides.

6. A hardened alloy steel composition as claimed in claim 5 consisting essentially of about .55% carbon, about .92% tungsten, about 5.19% molybdenum and about .95% vanadium with the remainder essentially iron.

7. A hardened alloy steel composition as claimed in claim 5 consisting essentially of about .5% carbon, about 1.82% tungsten, about 2.63% molybdenum, and about .93% vanadium with the remainder essentially iron.

8. A hardened alloy steel composition as claimed in claim 5 consisting essentially of about .53% carbon, about 5.49% molybdenum, and about 1.1% vanadium with the remainder essentially iron.

9. A hardened alloy steel composition as claimed in claim 5 consisting essentially of about .55% carbon, about 2.02% tungsten, about 2.60% molybdenum, about .95 vanadium and about 7.85% cobalt with the remainder essentially iron.

10. A hardened alloy steel composition as claimed in claim 5 consisting essentially of about .55% carbon, about 1.00% tungsten, about 5.00% molybdenum, about 92% vanadium and about 7.95% cobalt with the remainder essentially iron.

11. A hardened alloy steel composition as claimed in claim 5 consisting essentially of about .50% carbon, about 8.45% tungsten, about .21% molybdenum and about .97% vanadium with the remainder essentially iron.

References Cited UNITED STATES PATENTS 3,117,863 1/1964 Roberts et al. 126

OTHER REFERENCES Tool Steels, Roberts et al., 1962, relied on pp. 613-621 and 705-707.

CHARLES N. LOVELL, Primary Examiner U.S. Cl. X.R. 

